Web coating and doctoring apparatus



March 12, 1963 E. J. JUSTUS WEB COATING AND DOCTORING APPARATUS Filed Oct. 21, 1959 United States Patentfifihce 3,680,847 Patented Mar. 12, 1963 3,080,847 WEB COATING AND DOCTORING APPARATUS Edgar J. Justus, Beloit, Wis., assignor to Beloit Iron Works, Beloit, Wis., a corporation of Wisconsin Filed Oct. 21, 1959, Ser. No. 847,772 2 Claims. (calls-126) for any one or a number of different reasons, which may be improvements in feel, printabili-ty, brightness, gloss, opacity, smoothness, and in order to hide the surface of the paper. A machine well known to the art is termed the Trist or trailing blade coater, by means of which a paper web Wrapped about a rubber covered roll has coating emulsion applied thereto by a stationary trailing scraper blade angularly arranged relative to the surface of the roll and forming a duct or fountain, the width of which is determined by dykes, side walls or marginal restrictors mounted on the blade and adjustable therealong.

It is further now recognized that the trailing blade coater has certain inherent disadvantages, and one 'of these is that the dams or dykes result in an unnecessarily complicated construction; Then too, it is required that the doctor blade be replaced by a blade having a different degree of resiliency/if the doctor is to be used to obtain coating weight control to supplement solids content or viscosity variations, forlpurposes of control of coating weight. Additionally, if a machine break occurs, it is necessary to retract the doctor blade, after performing the time consuming step of either draining or dumping the reservoir. Persons skilled in the paper coating art are now aware of other disadvantages lying in utilization of the trailing blade coater, generally speaking the difiiculties named are among those discussed in any consideration of present coating methods.

It is accordingly an important aim of the instant invention to provide coating apparatus devoid of dam, fountain and related structure, and incorporating therein means carefully controlling the coating weight applied over a relatively wider range than normally obtained by devices known to the art.

Another object of this invention lies in the provision of a method of coating paper and like materials, featuring among the steps thereof removing excms coating material from a point closely adjacent its point of application, and discharging said excess coating directly to the coating applicator means.

', Still another object of the present invention is to provide apparatus for coating a traveling web moving in wrapping relation with a platen roller, andwhich comprises a plurality of applicator rollers in nip-defining relation one with the other, one of said applicator rolls defining a nip with the platen roller whereat coating material held by the applicator rolls is transferred to the of the coating color.

In the drawings, wherein like numerals designate like parts throughout the same:

FIGURE 1 is a more or less schematic view of apparatus constructed in accordance with the principles of this invention, and constituting one structural embodiment especially suited to practice the method of this invention; and

FIGURE 2 is a fragmentary end elevational view of the apparatus of FIGURE 1, and showing particularly trough means which may be employed at opposite ends of the applicator rolls to collect any overflow.

Referring now to the drawings, there is shown coating apparatus generally designated by the numeral 10 and comprising a platen roll 12 supported by a shaft means 14 and receiving a paper web or related sheet material 16 in wrapping relation therewith. The platen roll 12 is in nip-defining relationship at N-l with an applicator roll '18, which defines a nip N-2 with another applicator roll 20, the rolls 20 and 18 being hereinafter referred to as first and second applicator rolls, respectively.

The applicator rolls 18 and 20 are supported by shaft means 22 and 24, said shafts being received at both ends in. generally upright supporting arms 26 and 28 pivotally connected at 30 and 32 to bracket means or the like 34 and 36 attaching with fixed structure, which may be the floor.

The applicator rolls 18 and 20 may be seen to be in general horizontal alignment, and held in the valley defined by said rolls is a supply of coating material 38 in solution or emulsion form delivered to the nip N-2 by one or more nozzle means 40, communicating with pump means or the like P in the manner known to the art. In most applications, the rolls 18 and 20 are counterrotating, and during said rotation the coating material 38 is split at the nip N-Z into substantially two film portions, one-half of said film being carried by the surface of the applicator roll 18 in a counter-clockwise direction to the nip N1, whereat said film is trasferred to the traveling web 16. As will be described in detail later, the amount of coating material delivered by the applicator roll 18 to the nip N4 is controlled by the relative surface speeds of the rolls 18 and 2t), and by control of the pressures at the nip N-Z.

Coating material transferred to the paper web 16 at the nip N4 is immediately subsequent to application contacted by smoothing means generally designated by the numeral 42. Such smoothing means may comprise a doctor blade 44 mounted by holder means 46 pivotally supported at 48 by suitable structure 48a, so that said holder 46 may be tilted or swung in the directions indicated by the arrow thereon to vary the amount of pressure applied bythe doctor blade 44, thereby controlling the amount of excess coating material removed by the doctor blade 44. While the amount of coating material removed by the blade 44 of course depends upon the coating mix and the base stock used, generally speaking the blade may be adjusted to remove either a negligible amount of coating, or up to about 49% or more of the coating weight applied at the nip N-l. 1

It is to be observed that the doctor blade 44 is locate closely adjacent the nip N-l at the ofi-running side thereof, and is positioned sufficiently close to the point of application of coating material to avoid dewatering In addition, by reason of close proximity of the doctor blade 44 to the nip N4, any grit or hardened particles which may be present in the coating material as applied are immediately and effectively removed prior to drying of the coating on the paper web. As is appreciated, undue exposure of the coating material to air reduces the flow properties thereof,

2. Apparatus for coating a traveling web comprising, a pair of parallel rolls in horizontally opposed nipdefining relationship to form a first nip for containing a puddle of coating on the upper side of the nip, means for supplying coating to said puddle,

means for rotating said rolls with their nip-defining surfaces traveling downwardly,

a Web supporting backing roll positioned above and in nip-defining relationship with one of said parallel rolls to form a second nip and rotatable with the nip side traveling in an upward direction,

a doctor blade means close to said second nip positioned to be in doctor-ing engagement with a web carried on the uprunning side said backing roll and positioned above said first nip so that the excess coating removed from the web will flow downwardly and directly into said first nip,

and means controlling the speed of at least one of said parallel rolls to vary its speed relative to the other parallel roll whereby the weight of the coating applied to the web on the backing roll can be varied.

References Cited in the file of this patent UNITED STATES PATENTS 

1. APPARATUS FOR COATING A TRAVELING WEB COMPRISING, A PAIR OF PARALLEL ROLLS IN HORIZONTALLY OPPOSED NIPDEFINING RELATIONSHIP TO FORM A FIRST NIP FOR CONTAINING A PUDDLE OF COATING ON THE UPPER SIDE OF THE NIP, MEANS FOR SUPPLYING COATING TO SAID PUDDLE, MEANS FOR ROTATING SAID ROLLS WITH THEIR NIP-DEFINING SURFACES TRAVELING DOWNWARDLY, A WEB SUPPORTING BACKING ROLL POSITIONED ABOVE AND IN NIP-DEFINING RELATIONSHIP WITH ONE OF SAID PARALLEL ROLLS TO FORM A SECOND NIP AND ROTATABLE WITH THE NIP SIDE TRAVELING IN AN UPWARD DIRECTION, AND A DOCTOR BLADE MEANS CLOSE TO SAID SECOND NIP POSITIONED TO BE IN DOCTORING ENGAGEMENT WITH A WEB CARRIED ON THE UPRUNNING SIDE SAID BACKING ROLL AND POSITIONED ABOVE SAID FIRST NIP SO THAT THE EXCESS COATING REMOVED FROM THE WEB WILL FLOW DOWNWARDLY AND DIRECTLY INTO SAID FIRST NIP. 